This application is a Continuation-in-Part of the copending application Serial No. 07/320680, filed Mar. 8, 1989 now abandoned.
This invention relates to thermoplastic resin compositions and more particularly relates to improved blends of carbonate polymers and acrylonitrile-ethylene-propylene-diene rubber-styrene copolymers (AES) and a method of using the compositions.
More specifically, this invention relates to molding compositions comprising a blend of (1) carbonate polymers with (2) graft copolymers of ethylene-propylene-diene terpolymer (EPDM) or a EPDM-vinyl aromatic hydrocarbon copolymer with a mixture of acrylonitrile and a vinyl aromatic hydrocarbon and (3) core/shell graft copolymers of alkyl acrylate or butadiene or butadiene-vinyl aromatic hydrocarbon or butadiene-vinyl aromatic hydrocarbon-alkyl acrylate with optionally a second phase of vinyl aromatic hydrocarbon and a outer shell of alkyl (meth)acrylate.
Although polycarbonate/AES compositions have been found to be thermoplastically moldable under a broad range of injection molding conditions, only select polycarbonate blends are suitable for blow molding. This is due to the unique requirement of thermoplastic resin for blow molding operations.
In the conventional blow molding operation, as taught in U.S. Pat No. 4,652,602 and U.S. Pat. No. 4,474,999, a tube or parison of the heat softened thermoplastic blend may be extruded vertically downward into a mold. The extrudate is then pressed unto the mold surfaces with a pressurized gas flow (usually air or inert gas), shaping the heat softened resin. As appreciated by those skilled in the art, the successful molding of a given thermoplastic resin is dependent upon a number of factors, including the characteristics and physical properties of the heat softened resin. The length and diameter of the tube and the quantity of material forming the tube are limiting factors in determining the size and wall thickness of the object that can be molded by this process. The fluidity of the melt obtained from polycarbonate/AES blends, or the lack of melt strength as well as the paucity of extrudate swelling, serve to limit blow molding applications to relatively small, thin walled parts. These factors alone are of considerable importance in the successful blow molding of any resin, particularly in regard to the molding of large articles.
It is known from Japanese patent 58/59258 that resin compositions with good weld strength can be obtained from blends of linear polycarbonate resins, acrylonitrile-butadiene-styrene resins (ABS), and rubbery graft copolymer resins (MBS). However, this reference does not suggest the advantage of using acrylonitrile-ethylene-propylene-diene rubber-styrene copolymers, to control rubber placement. This patent is attempting to modify the ABS phase to improve the weldline by utilizing MBS resins containing 30-50% rubber and styrene in the outer shell. It is believed that having styrene in the outer shell helps to drive the MBS resins into the ABS phase where the added rubber helps to improve the poor weldline properties of the ABS.
It is further known from U.S. Pat. No. 4,677,162 that a moldable blend of both linear or branched polycarbonate resins (PC), acrylonitrile-butadiene-styrene resins (ABS), and rubbery graft copolymers (MBS) is useful to form articles with good impact and low gloss. However, this reference utilizes only ABS resins and does not recognize the advantage of using AES a more environmentally stable resin.